On Wed, May 25, 2016 at 2:12 PM, Baolin Wang <baolin.wang@xxxxxxxxxx> wrote:
> In dm-crypt, it need to map one bio to scatterlist for improving the
> hardware engine encryption efficiency. Thus this patch introduces the
> blk_bio_map_sg() function to map one bio with scatterlists.
>
> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxx>
> ---
> block/blk-merge.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
> include/linux/blkdev.h | 3 +++
> 2 files changed, 48 insertions(+)
>
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 2613531..9b92af4 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -417,6 +417,51 @@ single_segment:
> }
>
> /*
> + * map a bio to scatterlist, return number of sg entries setup.
> + */
> +int blk_bio_map_sg(struct request_queue *q, struct bio *bio,
> + struct scatterlist *sglist,
> + struct scatterlist **sg)
> +{
> + struct bio_vec bvec, bvprv = { NULL };
> + struct bvec_iter iter;
> + int nsegs, cluster;
> +
> + nsegs = 0;
> + cluster = blk_queue_cluster(q);
> +
> + if (bio->bi_rw & REQ_DISCARD) {
> + /*
> + * This is a hack - drivers should be neither modifying the
> + * biovec, nor relying on bi_vcnt - but because of
> + * blk_add_request_payload(), a discard bio may or may not have
> + * a payload we need to set up here (thank you Christoph) and
> + * bi_vcnt is really the only way of telling if we need to.
> + */
> +
> + if (bio->bi_vcnt)
> + goto single_segment;
> +
> + return 0;
> + }
> +
> + if (bio->bi_rw & REQ_WRITE_SAME) {
> +single_segment:
> + *sg = sglist;
> + bvec = bio_iovec(bio);
> + sg_set_page(*sg, bvec.bv_page, bvec.bv_len, bvec.bv_offset);
> + return 1;
> + }
> +
> + bio_for_each_segment(bvec, bio, iter)
> + __blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
> + &nsegs, &cluster);
> +
> + return nsegs;
> +}
> +EXPORT_SYMBOL(blk_bio_map_sg);
You can use __blk_bios_map_sg() to implement blk_bio_map_sg(),
then code duplication may be avoided.
> +
> +/*
> * map a request to scatterlist, return number of sg entries setup. Caller
> * must make sure sg can hold rq->nr_phys_segments entries
> */
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 1fd8fdf..e5de4f8 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -1013,6 +1013,9 @@ extern void blk_queue_write_cache(struct request_queue *q, bool enabled, bool fu
> extern struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev);
>
> extern int blk_rq_map_sg(struct request_queue *, struct request *, struct scatterlist *);
> +extern int blk_bio_map_sg(struct request_queue *q, struct bio *bio,
> + struct scatterlist *sglist,
> + struct scatterlist **sg);
> extern void blk_dump_rq_flags(struct request *, char *);
> extern long nr_blockdev_pages(void);
>
> --
> 1.7.9.5
>
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